Rename IoStream to OutDest (#12433)

# Description
I spent a while trying to come up with a good name for what is currently
`IoStream`. Looking back, this name is not the best, because it:
1. Implies that it is a stream, when it all it really does is specify
the output destination for a stream/pipeline.
2. Implies that it handles input and output, when it really only handles
output.

So, this PR renames `IoStream` to `OutDest` instead, which should be
more clear.

crates/nu-protocol/src/ast/block.rs

@@ -1,5 +1,5 @@
 use super::Pipeline;
-use crate::{engine::EngineState, IoStream, Signature, Span, Type, VarId};
+use crate::{engine::EngineState, OutDest, Signature, Span, Type, VarId};
 use serde::{Deserialize, Serialize};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -20,12 +20,12 @@ impl Block {
         self.pipelines.is_empty()
     }
 
-    pub fn stdio_redirect(
+    pub fn pipe_redirection(
         &self,
         engine_state: &EngineState,
-    ) -> (Option<IoStream>, Option<IoStream>) {
+    ) -> (Option<OutDest>, Option<OutDest>) {
         if let Some(first) = self.pipelines.first() {
-            first.stdio_redirect(engine_state)
+            first.pipe_redirection(engine_state)
         } else {
             (None, None)
         }

crates/nu-protocol/src/ast/expr.rs

@@ -6,8 +6,8 @@ use super::{
     RangeOperator,
 };
 use crate::{
-    ast::ImportPattern, ast::Unit, engine::EngineState, BlockId, IoStream, Signature, Span,
-    Spanned, VarId,
+    ast::ImportPattern, ast::Unit, engine::EngineState, BlockId, OutDest, Signature, Span, Spanned,
+    VarId,
 };
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -56,19 +56,19 @@ pub enum Expr {
 }
 
 impl Expr {
-    pub fn stdio_redirect(
+    pub fn pipe_redirection(
         &self,
         engine_state: &EngineState,
-    ) -> (Option<IoStream>, Option<IoStream>) {
+    ) -> (Option<OutDest>, Option<OutDest>) {
         // Usages of `$in` will be wrapped by a `collect` call by the parser,
         // so we do not have to worry about that when considering
         // which of the expressions below may consume pipeline output.
         match self {
-            Expr::Call(call) => engine_state.get_decl(call.decl_id).stdio_redirect(),
+            Expr::Call(call) => engine_state.get_decl(call.decl_id).pipe_redirection(),
             Expr::Subexpression(block_id) | Expr::Block(block_id) => engine_state
                 .get_block(*block_id)
-                .stdio_redirect(engine_state),
-            Expr::FullCellPath(cell_path) => cell_path.head.expr.stdio_redirect(engine_state),
+                .pipe_redirection(engine_state),
+            Expr::FullCellPath(cell_path) => cell_path.head.expr.pipe_redirection(engine_state),
             Expr::Bool(_)
             | Expr::Int(_)
             | Expr::Float(_)
@@ -89,7 +89,7 @@ impl Expr {
             | Expr::Nothing => {
                 // These expressions do not use the output of the pipeline in any meaningful way,
                 // so we can discard the previous output by redirecting it to `Null`.
-                (Some(IoStream::Null), None)
+                (Some(OutDest::Null), None)
             }
             Expr::VarDecl(_)
             | Expr::Operator(_)
@@ -103,7 +103,7 @@ impl Expr {
             | Expr::Garbage => {
                 // These should be impossible to pipe to,
                 // but even it is, the pipeline output is not used in any way.
-                (Some(IoStream::Null), None)
+                (Some(OutDest::Null), None)
             }
             Expr::RowCondition(_) | Expr::MatchBlock(_) => {
                 // These should be impossible to pipe to,

crates/nu-protocol/src/ast/pipeline.rs

@@ -1,7 +1,7 @@
 use crate::{
     ast::Expression,
     engine::{EngineState, StateWorkingSet},
-    IoStream, Span,
+    OutDest, Span,
 };
 use serde::{Deserialize, Serialize};
 use std::fmt::Display;
@@ -118,11 +118,11 @@ impl PipelineElement {
         }
     }
 
-    pub fn stdio_redirect(
+    pub fn pipe_redirection(
         &self,
         engine_state: &EngineState,
-    ) -> (Option<IoStream>, Option<IoStream>) {
-        self.expr.expr.stdio_redirect(engine_state)
+    ) -> (Option<OutDest>, Option<OutDest>) {
+        self.expr.expr.pipe_redirection(engine_state)
     }
 }
 
@@ -164,12 +164,12 @@ impl Pipeline {
         self.elements.is_empty()
     }
 
-    pub fn stdio_redirect(
+    pub fn pipe_redirection(
         &self,
         engine_state: &EngineState,
-    ) -> (Option<IoStream>, Option<IoStream>) {
+    ) -> (Option<OutDest>, Option<OutDest>) {
         if let Some(first) = self.elements.first() {
-            first.stdio_redirect(engine_state)
+            first.pipe_redirection(engine_state)
         } else {
             (None, None)
         }